I have hCG that I haven’t mixed yet. Does the expiration start after you’ve mixed it?

The expiration is for the hCG whether mixed or not. Per the pharmacy testing rules, you wouldn’t want to use your vial beyond the expiration or beyond use date listed on the vial (again, this is no matter if you mix it right away or at a later time- the date on the vial is cut off point for using it period). Normally, the expiration of the solution once you mix it will expire before the date on the bottle anyway in the sense that once you mix your hCG, our understanding is you want to use up the vial within about 30 days before the potency will be too lost to be of any further benefit.